Various methods for manufacturing a ceramic circuit board are available, and improvement for lower cost, higher precision, and higher reliability has been sought. Conventionally, for such a ceramic circuit board, gold, silver, copper, or aluminum has been selected as a material for a conductor layer, and a method using a metal foil or a metal paste, PVD (sputtering or vacuum vapor deposition), or CVD has been adopted as a method for forming a conductor layer. A method of etching a conductor layer or a method of printing a paste in a form of a circuit has been adopted as a method for forming a conductor layer in a circuit pattern.
In forming a conductor layer, since PVD or CVD is a vacuum process, it is disadvantageous in high cost and insufficient adhesiveness. In using a metal foil, an adhesive should be used for fixing a metal foil to a ceramic substrate, and deterioration thereof tends to be disadvantageous in terms of long-term stability.
In using a metal paste, such a precious metal as gold, silver, or copper has mainly generally been used, however, cost thereof is high. In addition, migration in a case of silver or increase in resistance value due to oxidation in a case of copper is disadvantageous.
As one of methods for solving the problems in using a metal paste, WO2010/100893 (hereinafter PTD 1) has proposed a method using an aluminum paste.
A specific method of forming a conductor layer by using a metal paste includes a method of printing a metal paste in a form of a circuit and a method of applying a metal paste all over a surface, firing the metal paste to thereby obtain a conductor layer, and thereafter etching the conductor layer. It has been known, however, that etching allows formation of a circuit with higher precision than printing in a form of a circuit because of printability or because of absence of influence by a particle size of metal particles in the metal paste.
In order to provide adhesiveness to a substrate in obtaining a conductor layer by firing the metal paste, generally, glass frit containing silicon is added to the paste and the paste is fired, to thereby obtain a conductor layer containing silicon.
In common etching, however, it is difficult to completely remove the conductor layer containing silicon from the surface of the substrate. Therefore, the conductor layer containing silicon remains as a residue also in an etched portion and reliability in insulation between interconnections may be lowered. As a method of removing the residue of the conductor layer, as shown in Japanese Patent Laying-Open No. 2010-278410 (hereinafter PTD 2), a method of subjecting the etched portion to sandblast treatment has been proposed.